81901681 has 4 divisors (see below), whose sum is σ = 82241764. Its totient is φ = 81561600.

The previous prime is 81901667. The next prime is 81901691. The reversal of 81901681 is 18610918.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 67914081 + 13987600 = 8241^2 + 3740^2 .

It is a cyclic number.

It is not a de Polignac number, because 81901681 - 2⁵ = 81901649 is a prime.

It is a super-2 number, since 2×81901681² = 13415770701251522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81901601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 169680 + ... + 170161.

It is an arithmetic number, because the mean of its divisors is an integer number (20560441).

Almost surely, 2^81901681 is an apocalyptic number.

It is an amenable number.

81901681 is a deficient number, since it is larger than the sum of its proper divisors (340083).

81901681 is a wasteful number, since it uses less digits than its factorization.

81901681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 340082.

The product of its (nonzero) digits is 3456, while the sum is 34.

The square root of 81901681 is about 9049.9547512681. The cubic root of 81901681 is about 434.2744429239.

The spelling of 81901681 in words is "eighty-one million, nine hundred one thousand, six hundred eighty-one".